The present disclosure relates generally to multipole circuit breakers, and particularly to neutral poles for use in multipole circuit breakers.
Multipole circuit breakers configured to protect multiphase electrical circuits are known in the electrical circuit protection industry. The variety of constructions of multipole circuit breakers include blow open and non-blow open contact arms, overcentering and non-overcentering contact arms, single contact pair arrangements with the contact pair at one end of a contact arm and a pivot at the other end thereof, double contact pair arrangements (referred to as rotary breakers) with a contact pair at each end of a contact arm and a contact arm pivot intermediate (typically centrally located between) the two ends, single housing constructions with the circuit breaker components housed within a single case and cover, and cassette type constructions (referred to as cassette breakers) with the current carrying components of each phase housed within a phase cassette and each phase cassette housed within a case and cover that also houses the operating mechanism. Multipole circuit breakers are generally available in two, three, and four pole arrangements, with the two and three pole arrangements being commonly used in two and three phase circuits, respectively. Four pole arrangements are typically employed on three phase circuits having switching neutrals, where the fourth pole operates to open and close the neutral circuit in a coordinated arrangement with the opening and closing of the primary circuit phases. Some fourth pole neutrals have identical constructions to the phase poles and are simply appended onto an outer pole by way of an extended crossbar or drive rod. The combination, however, of a phase pole construction and an extended drive rod typically results in less contact depression in the neutral pole due to the additional strain on the drive rod, the fourth pole neutral being that much further removed from the operating mechanism. To address the anticipated reduction in contact depression, design modifications within the circuit breaker may be employed. Other fourth pole neutrals have supplemental fourth pole operating mechanisms specifically arranged for operating only the fourth pole neutral. While a supplemental fourth pole operating mechanism is effective in controlling lost contact depression to due additional strain, it also typically involves higher complexity and cost compared to a construction without a supplemental operating mechanism. In view of present fourth pole neutral arrangements, it is desirable to have a fourth pole neutral that overcomes the above disadvantages.
In one embodiment, a neutral pole for a multipole circuit breaker is disclosed. The circuit breaker includes a housing, a plurality of contact arms for opening and closing an electrical circuit and an operating mechanism for driving the contact arms. The neutral pole includes a neutral housing, a conduction path within the neutral housing having a neutral arm arranged for opening and closing the conduction path, a bias spring configured to exert a first bias moment on the neutral arm when the conduction path is closed, a spring support configured to support the bias spring, a rotor pivotally arranged within the neutral housing and configured to displace the neutral arm and open the conduction path, and a drive pin configured to couple the rotor to the multipole circuit breaker. The spring support is fixedly arranged at the neutral housing. The rotor is responsive to the opening and closing action of the operating mechanism of the multipole circuit breaker.
In another embodiment, a multipole circuit breaker includes a main housing, a main conduction path having contact arms configured to open and close an electrical circuit, an operating mechanism configured to drive the contact arms, and a neutral pole. The neutral pole includes a neutral housing in fixed arrangement with the main housing, a neutral conduction path within the neutral housing having a neutral arm arranged to open and close the neutral conduction path, a bias spring configured to exert a first bias force on said neutral arm when said neutral conduction path is closed, a spring support configured to support the bias spring, a rotor pivotally arranged within said neutral housing and arranged to displace the neutral arm and to open the neutral conduction path, and a drive pin configured to couple the rotor to the operating mechanism. The spring support is fixedly coupled to the neutral housing. The rotor is responsive to the opening and closing action of the operating mechanism.
In a further embodiment, a method for opening a neutral pole of a multipole circuit breaker includes receiving an opening command at the neutral pole from the multipole circuit breaker, and responding to the opening command to open the neutral conduction path by rotating a neutral rotor a first angular displacement under no load from a set of neutral bias springs and a second angular displacement under load from the set of neutral bias springs.